Toll-like receptors (TLRs), have been linked to the potent innate immune response and recognize distinct structural components that are unique to pathogens; this interaction drives the immune system into an activated state, with short- and long-term consequences. There is significant interest in developing agonists and antagonists of TLRs since the pharmacological manipulation of innate immune responses may lead to more effective vaccines and novel therapeutic approaches to autoimmune, atopic, malignant and infectious diseases. The first microbial product discovered to be a Toll-like receptor agonist was LPS, a bacterial membrane component specific to gram negative bacteria, which activates Toll-like receptor 4 (TLR-4). Although LPS is a potent immunomodulatory agent, its medicinal use is limited due to its extreme toxicity, including the induction of systemic inflammatory response syndrome. The biologically active endotoxic sub-structural moiety of LPS is lipid-A, a phosphorylated, multiply fatty-acid-acylated glucosamine disaccharide that serves to anchor the entire structure in the outer membrane of Gram-negative bacteria. The toxic effects of lipid A can be ameliorated by selective chemical modification of lipid A to produce monophosphoryl lipid A compounds (MPL™ immunostimulant; Corixa Corporation; Seattle, Wash.). Methods of making and using MPL™ immunostimulant and structurally like compounds in vaccine adjuvant and other applications have been described (see, for example, U.S. Pat. Nos. 4,436,727; 4,877,611; 4,866,034 and 4,912,094; 4,987,237; Johnson et al., J Med Chem 42:4640-4649 (1999); Ulich and Myers, in Vaccine Design: The Subunit and Adjuvant Approach; Powell and Newman, Eds.; Plenum: New York, 495-524, 1995). In particular, these and other references demonstrated that MPL™ immunostimulant and related compounds had significant adjuvant activities when used in vaccine formulations with protein and carbohydrate antigens for enhancing humoral and/or cell-mediated immunity to the antigens and interact with Toll-like receptors.
Drawing from experience with MPL™ immunostimulant and other bacterial cell wall components, a family of novel synthetic compounds, the aminoalkyl glucosaminide phosphates (AGPs), were developed. AGP compounds also interact with TLR-4, as agonists and antagonists. AGPs include both acyclic and cyclic compounds (U.S. Pat. Nos. 6,113,918, and 6,303,347, WO 98/50399 published Oct. 12, 1998, WO 01/34617, published May 17, 2001, WO 01/90129, published Nov. 29, 2001, and WO 02/12258, published Feb. 14, 2002). Like MPL™ immunostimulant, these compounds have been demonstrated to retain significant adjuvant characteristics when formulated with antigens in vaccine compositions and, in addition, have similar or improved toxicity profiles when compared with MPL™ immunostimulant. AGPs also demonstrate mucosal adjuvant activity and are effective in the absence of antigen, making them attractive compounds for the prophylactic and/or therapeutic use.
Another significant advantage offered by the AGPs over MPL™ immunostimulant and the like is that the AGPs are readily producible on a commercial scale by synthetic means. Since they are produced synthetically AGPs are free of trace biological contaminants found in MPL. As such AGPs would have an advantage over MPL as vaccine adjuvants in certain settings, such as in pediatric immunization protocols where adjuvant pyrogenicity must be minimized. However, because AGPs are chemically synthesized, less then optimum compound stability may lead to the accumulation of degradation products that may result in variable biological activity and stability from lot-to-lot. From the standpoint of developing GMP processes for manufacturing of materials for human clinical trials, lot stability and lot-to-lot variability are major issues. Therefore, compounds that have increased biological activity in comparison to MPL™ immunostimulant and the like, interact with toll-like receptors and/or are optimized for large scale GPL synthesis are desirable. The present invention addresses these needs and more by providing compounds modified to enhanced biological activity, stability with increased resistance to enzymatic and chemical degradation, and/or improved safety profiles.